Why Fixed window algorithm in Rest API? - Purpose & Use Cases

The Big Idea

What if you could stop overloads and unfair blocks with just a simple time-based counting trick?

The Scenario

Imagine you run a busy online store and want to limit how many times a user can place an order in one minute to prevent overload.

Without automation, you try to track each user's requests by hand, counting every order and checking the time manually.

The Problem

This manual counting is slow and confusing.

You might miss some requests or count them twice.

It's hard to keep track of many users at once, and mistakes can cause your system to crash or unfairly block users.

The Solution

The Fixed window algorithm automatically counts requests in fixed time blocks, like one-minute windows.

It resets the count every minute, making it easy to check if a user has reached the limit.

This keeps your system safe and fair without extra work.

Before vs After

✗ Before

if user_requests_in_last_minute < limit:
    allow_request()
else:
    block_request()

✓ After

window_start = current_time - (current_time % window_size)
count = get_request_count(user, window_start)
if count < limit:
    allow_request()
else:
    block_request()

What It Enables

This algorithm lets your system handle many users smoothly by controlling request rates automatically and fairly.

Real Life Example

Popular websites use the Fixed window algorithm to stop users from sending too many login attempts in a short time, protecting against hacking.

Key Takeaways

Manual counting of requests is slow and error-prone.

Fixed window algorithm divides time into blocks and counts requests per block.

This method keeps systems stable and fair under heavy use.